ERBB2 and bone metastasis: In terms of bone metastases, univariate and multivariate analysis showed that the probability of bone metastasis of HR+/HER2− and HR+/HER2+ subtypes was significantly higher than that of the HR−/HER2+ and HR−/HER2− subtypes, while there was no significant difference in the probability of bone metastasis between HR+/HER2− and HR+/HER2+ (Table 3; Figure 2).